In the current IEEE 802.11 standard, an authenticated device (STA) wishing to join an infrastructure network needs to first send an Association Request to an access point (AP).
The STA is considered to be associated with the AP when an Association Response with a status code value of ‘successful’ is acknowledged by the STA. The association process 100 is illustrated in FIG. 1 for a STA 102 successfully associated with an AP 104.
As seen in FIG. 1, the STA 102 sends an Association Request 106 to the AP 104. In response, the AP 106 sends an Association Response including an Association ID (AID) 108 to the STA 102. Upon receiving the Association Response including the AID 108, the STA 102 sends an acknowledgement frame (ACK) 110 to the AP 104. Thus, each successfully-associated STA has an AID. At times, the STA may also need to re-associate with the AP (e.g. after AP power down). The procedure of re-association may be similar to FIG. 1. In re-association, the AP may re-assign another AID to the STA.
The IEEE 802.11 supports power-saving mode operation. A STA may go to power saving (PS) mode and only listen periodically to beacon messages to check whether there is any data buffered for it in the AP. If there is data for a STA while it is in PS mode, the AP buffers the data and informs the STA. This is achieved via the traffic indication map (TIM) information element (IE) in the beacon message. The TIM element format includes a partial virtual bitmap (or referred to as the traffic indication virtual bitmap).
The traffic indication virtual bitmap consists of a maximum of 2008 bits. Bit 1 to Bit 2007 in the traffic indication virtual bitmap corresponds to STA with AID 1 to 2007, respectively. When the bit is set to 1, it indicates that there is data buffered in the AP for the corresponding STA. When the bit is 0, it indicates that there is no data buffered in the AP for the corresponding STA. AID 0 is used to indicate broadcast/multicast, and is indicated in the Bit 0 of the bitmap control field. The partial virtual bitmap does not always need to start from AID 0. This is controlled by the offset value in bitmap control field, which indicates the starting AID of the partial virtual bitmap.
In the IEEE 802.11AH meter-to-pole use case, up to 6000 STAs per AP need to be supported. However, as described above, the current IEEE 802.11 standard is only able to address up to 2007 STAs in power-saving (PS) mode. The requirement to support about 6000 STAs mainly affects the PS STAs as there is no impact on the active STAs, since they are not addressed by AID and TIM.
To support, for example, 6000 STAs, additional information may be tagged to each device, where multiple STAs may share a single AID, and the STAs are differentiated by the additional ‘Device Information’ element. However, for each beacon, the group of STAs sharing a single AID is addressed together by the corresponding TIM bit, and each individual STA is not addressed separately.
The TIM definition may also be altered to support 6000 STAs. For example, rather than using all the 2007 bits as traffic indication bitmap, two bits may be used to indicate grouping. For each TIM, one group (as indicated by the two grouping bits) is addressed. The STAs belonging to the group is addressed by the remaining 2005 bits. This approach however requires the current definition of TIM to be changed, and allows addressing of only one group of STAs.
Alternatively, the STAs may be grouped based on application type or location. Each group may contain up to 2007 STAs and is assigned a unique BSSID (basic service set identification), as described below in the beacon frame format of Table 3. Different groups may be addressed by using the BSSID for each corresponding group in the beacon. The interpretation of the TIM remains the same. However, in this approach, multiple BSSIDs may be needed and each beacon may only address one particular group. Furthermore, STAs have to check every beacon in order to find its own BSSID group.
The STAs may also be assigned different beacon intervals with different offsets. Multiple STAs may be allowed to share one AID, but they are unable wake up at the same time. At each beacon, a maximum of one STA from the sets of STAs sharing one AID may wake up. However, in this approach, the AP may have to keep the states of the associated STAs in order to set the TIM correctly, the STAs may lose control of its wake up interval, and additional signaling may be needed during association to specify the wake up interval and offset for each STA.
Thus, there is a need to provide mechanisms seeking to address at least the problems above to efficiently address multiple STAs.